1. Field of the Invention
The invention relates to the field of orthopedic devices and in particular to devices for measurement of mandibular function.
2. Description of the Prior Art
TMJ examinations are routinely done both diagnostically as well as to measure therapeutic outcome of treatment. In temporomandibular joint (TMJ) examinations the patient is asked to open his or her mouth as wide as possible to provide an indicator of mandibular function. Measurement of the opening is used diagnostically to determine a number of different diseases or dysfunctions of the temporomandibular joint.
Many different types of apparatus and methods have been devised to measure the opening or movement of the double joint mandible. Electro-optical systems have been shown by Kataoka et.al., "Mandibular Motion Diagnostic Device," U.S. Pat. No. 4,447,207 (1984); and electromechanical systems are described by Burckhardt, "Dental Device," U.S. Pat. No. 4,687,003 (1987) and Pameijer, "Method and Apparatus for Measuring and Recording Three Dimensional Condylermovements of the Mandible," U.S. Pat. No. 4,014,097 (1977). However, all of these systems only measure distances or positions and none are capable of a simultaneous force measurement. Still further they are complex, expensive and ill adapted to general clinical practice.
Devices are also known which apply a force to the jaw for therapeutic purposes, but have no capability of quantifying the force applied or simultaneously correlating a distance with it. See, Beeuwkes, III et.al., "Passive Jaw Exerciser," U.S. Pat. No. 4,909,502 (1990) and Fontenot, "Involuntary Oscillator System for the Mandible," U.S. Pat. No. 4,883,046 (1989) sold as the Transjaw by Transjaw Company of Houston, Tex.
The distance of jaw opening is defined as the active stretch distance. Typically, the doctor inserts his thumb and index finger into the patient's mouth between the upper and lower jaws to stretch the jaws apart as far as possible. The physician assesses both the distance, termed the border position, and the "end-feel", the amount of force required to achieve the border position. Through long and repeated experience, the physician develops by trial and error a sense for the "end-feel", and therefore assesses temporomandibular joint dysfunction based upon the rigidity, softness and other characteristics of the feel of the jaw opening when it reaches its end point. Similar manual application of force to a transducer mounted the patient's teeth and physician's thumb to measure the end force, and the use of light sensitive cells in combination with a recording oscilloscope to measure the border position is shown by J. Hesse et. al., "Craniomandibular Stiffness Toward Maximum Mouth Opening in Healthy Subjects: A Clinical and Experimental Investigation," Journal of Craniomandibular Disorders: Facial & Oral Pain, Vol. 4, No. 4, page 257-65 ( 1990). This technique is impractical as a clinical tool because the equipment is relatively sophisticated, largely not portable, expensive and not commonly available in a dentist's office.
As a matter of clinical practice border postion and end point feel are empirically determined by feel. In some cases the border position is determined by joint dysfunction or in other cases the border position may be limited by muscular dysfunction, each having a different end field. Only the border position is quantitative, when measured by a ruler or measuring rule, and the detection of the "end-feel" is entirely qualitative. Clinical diagnosis is imprecise using this prior art technique and can be developed only through long periods of experience by trial and error, in other words physician must develop an educated feel for the pair of parameters, force and distance, associated with mandible opening. While devices for simultaneously measuring force and correlated body movement, comprising the movement of multiple numbers of joints, are known, see Farrar, Jr., "Orthopedic Muscle Testing Apparatus," U.S. Pat. No. 3,922,918 (1975), no practical clinical device is known which simultaneously measures border position and end feel in the temporomandibular joint.
Therefore, what is needed is some type of means whereby force and distance of a mandible opening can be accurately, quickly and simultaneously made in a practical clinical setting.